Aircraft sustaining rotor blade with suction system for boundary layer control



Oct. 27, 1953 CAMPBELL 2,656,892

. S. AIRCRAFT SUSTAINING ROTOR BLADE WI'TH SUCTION Filed 00?,- 19, 1948 SYSTEM FOR BOUNDARY LAYER CONTROL 2 Sheets-Sheet 1 3m entor attorney 5 Oct. 27, 1953 H. s. CAMPBELL 2,656,892

AIRCRAFT SUSTAINING ROTOR BLADE WITH SUCTION SYSTEM FOR BOUNDARY LAYER CONTROL 2 Sheets-Sheet 2 Filed Oct. 19, 1948 Jrwentor flow. QZW a ttorncgs Patented Oct. 27, 1953 AIRCRAFT SU STAININ G ROTOR BLADE WITH- SUGTION SYSTEM FOR-BOUND- LAYER CONTROL Harris' .S. Campbell, Bryn .Athyn,.';Pa.,.assign0r to Ailtogilo C ompan-y of America;Philadelphia,.,

Pa., a corporationiof Delaware. Applicationwctobertm, 1948; Serial No;55,254 8fbla'imsa (01. 170-1354) This: invention relates to aircraft sustaining.- crotors; and: is particularly.. concerned. with a. novel sustaining rotor blade-construction espe-. cially adapted for use in a driven rotor,'.. for instance; ashelicopterirotor sdrivenz' either through the :hubor by-means of 20118 or morejet-.driving} devices. mounted on thetbladesv Certain; fea-s turesof the I invention are especially, concerned withbthetypeof:rotorrin which the-:blades carry jet-driving. devices.

In :sustainingr rotors lot 1. the-character.- referred. toaaetendency;developsaforf the. tip; region :of :the blades lto 'sstall, under; certain conditions of.op eratiomaespeciallyvwhere the. rotor blades-aarer of. profile. providing a particularly advantageous 1 litt-fito-draglratio. It; is..- a principal object; of; the present invention to provide a system; of;

boundary layer control applicable to theetiprega'on/of; suohurotorfb-lades, whereby to minimize thevtendencyl for blade stalling.

Another; object. of .the:.invention. is concerned wit ..the

tip region Ofthe blade; providing. for difierenti suction elfect-in difierent regions of. the slotting lengthwise otithe blade.

In... accordance: with still another. feature. of the" invention, it is. contemplated that. the. air

supply... to a blade tip jet-be derived fromia duct.

withinthe blade, which .duct is also utilizedsas a means forsettingnp suction-for. drawingein into blade slots, and layer control.

th'ereb'y,achievingmoundary How. the .fo'regoingand loth'er objectsand -adr."

vantages. are. attained-.willl. appear more. fully.

from the following. description, referring. to the:

accompanying drawings; in whichlfigurel. is.-an outlineplan view of a.rotat ive the .tip region thereof to illustrate .certairnparts lying therein;

FigureZ-Ifisa sideelevational viewof the aircrafit shown in .Figure 1?;

Figure 311s. a planrview tolan.enlarged..scale. of. rotor blade. according .to, view including. amodified. and of i the boundary layer. which latterl is? broken out and Q poratedin. the-arrangement or Figures 1 and 2; and

View onwant. of-Figure 3, anddllustratingpne form of blade section pref.-- erably lutilizedpwhich formlmay also be incor.

here mentioned, however; thatv Figure: 5. is an outline :view of anotherblade profile which: may. besemployed according to theinvention-.1.

Referrin'gzfirst tooEigures land .2, the body of a-.he1icopter isindicated at 6.. The helicopter.

mayv'be providedwwith appropriate. landingv gear. such1as=thewheels indicated; at 'I-T-and :8; and.

hasla fitting: ;l6.pivoted by;.means otla-ldragpivotl theedragtlink in. turn being,

llto a drag linlclB; pivoted by; a :flapping pivot l 9 .-to a pair. of apertured lugs. file-Mirprojectingr fromlthe hub. l2. Provision may alsobe more :fully. herebelow in-connection .with the embodiment of: Figure Before considering.the-arrangement of slotting and suction. mechanism emp1oyed.-. attthe. tip, ofv the bladesl in the embodiments .oflFiigu-res land-2, reference is made fication .Of.Figl1I8:=3. Here of 7 which has. an fitting 2-I This-.fork= 22: is connected control .arm. 2]; .w-hich change housing 2|. beconnected by suitable-.linkagewith.amniversalvertically; shiftable,

concurrently. Since such pitchicontrolmechae' nismszare now.'well understood inthissart; they, need-not be considered. in detailihereinr It is. the: problem of;

.ignre 1,,which hub, and; the roottend. of the.

madeaforcontrollablevariation ofthe blade pitch, in ,themannerdescribed to certain features of the modi-- it will beseen that a. blade! 4a. is-built -.up .-onx alspar. l 5w theqrootlend a with the hub 2.3 by, auniversal. joint 2 incorporating; both flapping and drag, pivots: The .bIadeein the arrangement .berhub driven, asbyya gear 25 secured to the hub 1 and. a cooperating drivinga pinionili. Control-led; variation ofithe bladepitch angle is obtainable bymeans of: the-1 is secured to.- the pitch Such a controlarm mayy blade tip stalling is ordinarily aggravated in a rotor system incorporating provision for cyclic variation of blade pitch (utilized for purposes of maneuvering the aircraft); and therefore the boundary layer control system of the present invention is of especial utility in a rotor system incorporating such blade pitch control.

As best seen in Figures 3 and 4, the profile of one form of blade preferably utilized, is one having a convexly curved lower surface 28 and an upper surface which is in general also convexly curved, as indicated at 29, but which has an abrupt reflex or reversely curved portion 38 located chordwise of the blade intermediate the trailing edge and the mid region. The blade section illustrated in Figure 4 is one having an unusually favorable lift-to-drag ratio when boundary layer control by suction is applied to the abruptly reversely curved portion 35. this portion of the blade is slotted, as indicated at 3|. As seen in Figure 3, the interior of the tip portion of the blade is provided with a series of partitions 32 which extend forwardly from the trailing edge of the blade and curve outwardly, the outer portions thereof being in spaced parallel relation, whereby a plurality of individual ducts are formed within the blade, each communicating with a portion of the slotted region of the tip. By differently proportioning the several ducts, different suction effects may be obtained at different portions of the slotted region of the blade. During rotation of the rotor, the columns of air within the ducts are acted upon by centrifugal force and the air is discharged radially outwardly.

In order to secure a substantial suction effect, the present invention provides for the employment of a blade tip extension, projecting beyond the tip of the blade proper, in which extension the ducts are continued, so as to provide columns of air of appreciable length to be acted upon by centrifugal force. This extension appears in Figures 3 and 4 at 33, and from Figure 4 it will be seen that the blade tip extension is of appreciably narrower chord dimension than the tip portion of the blade, preferably being not in excess of about one-half of the chord dimension of the blade tip. Moreover, as seen in Figure 4, the profile of the tip portion 33 is advantageously of the so-called wedge shaped contour, having a relatively sharp leading as well as trailing edge, this being a type of airfoil section particularly suitable to very high air speeds ranging into the transonic and even supersonic speeds.

With further reference to the blade of Figures 3 and 4, it is noted that a portion of the blade inboard of the slotted region is advantageously built up upon the spar l5a as by employment of ribs such as shown at M. The spar tube l5a may be terminated in the region of the slotted portion of the blade and provided with a fitting such as shown at 35 for connection with the tip portion of the blade, which is made up of the partitions 32 and appropriate upper and lower blade surface sheets.

It is contemplated that the profile or section of the blade tip and also of the blade tip extension illustrated in Figures 3 and i also be employed in the arrangement of Figures 1 and 2, and various parts thereof are therefore only shown in outline in Figs. 1 and 2. In the embodi ment of Figures 1 and 2, however, the blades carry jet driving devices such as indicated at 38. The specific construction of such jet driving devices forms no part of the present invention per se, but according to the invention, the outboard ends of the suction ducts formed within the blade tip extension 33 deliver air into the jet devices, for the burning of fuel therein. Thus, in this arrangement, the ducts are utilized not only for developing suction to provide boundary layer control, but in addition for feed of air to the jet driving devices. It may be noted that in. Figure l the slotted region of the blade is of somewhat greater length than that appearing in Figure 3. This may be advantageous, especially in a jet driven rotor, since the blade tip speed in jet driven rotors is ordinarily higher than in hub driven rotors, as a result of which a greater portion of the tip of the blade approaches the critical speeds at which drag increases. Extending the boundary layer control aids in reducing such drag. It will further be noted that whereas in the arrangement of Figure 3, five ducts are provided in the slotted region of the blade, in the embodiment of Figure 1, six of such ducts are used.

Figure 5 is illustrative of another blade profile which may advantageously be employed in association with the boundary layer control system of the present invention. In this figure, the upper and lower surfaces 3'! and 38 of the blade are of similar curvature, each having an abrupt,

change in curvature in a region intermediate the trailing edge of the blade and the mid region thereof, as shown at 39 and 40. In this form of blade, it is preferred to provide slotting 31a, not only in the upper surface of the blade, but also in the lower surface thereof, in the regions 3% and 40.

I claim:

1. For an aircraft sustaining rotor, a rotor blade having, at least in the tip region of the blade, an abrupt reversely curved portion in the upper surface thereof, said portion being located chordwise intermediate the trailing edge and the mid region of the blade, and the said reversely curved portion having a plurality of slots for intake of air, and air suction mechanism comprising ducts individually communicating with said slots and extending within the blade radially outwardly from the slots for air discharge under the action of centrifugal force acting on the columns of air in the ducts.

2. A construction according to claim 1 and further including a blade tip extension of narrow chord as compared with the tip region of the blade, the said ducts being extended through said extension.

3. A construction according to claim 1 and further including a jet driving device mounted on the blade and receiving air from the outboard ends of said ducts.

4. For an aircraft sustaining rotor, a rotor blade having, at least in the tip region of the blade, an abrupt reversely curved portion in the upper surface thereof, said portion being located chordwise intermediate the trailing edge and the mid region of the blade, and intake in said reversely curved portion, and air suction mechanism comprising a duct communicating radiallyoutwardly Within the tip portion of the blade, and a blade tip extension of narrow chord as compared with the tip region of the blade, the said duct being extended through said extension for air discharge at the tip thereof under the action of centrifugal force acting on the column of air in the duct.

having a slotted air with said slotted air intake and extending v 5. For an aircraft sustaining rotor, a rotor blade having in the tip region of the blade a plurality of slots for the intake of air located chordwise intermediate the trailing edge and the mid region of the blade, and air suction mechanism comprising ducts individually communicating with said slots and extending Within the blade radially outwardly from the slots for air discharge under the action of centrifugal force acting on the columns of air in the ducts.

6. A construction according to claim 5 and further including a blade tip extension of narrow chord as compared with the tip region of the blade, the said ducts being extended through said extension.

7. A construction according to claim '5 and further including a jet driving device mounted on the blade and receiving air from the outboard ends of said ducts.

8. A construction in accordance with claim 4 and further including a jet driving device mounted at the tip of said blade tip extension.

HARRIS S. CAMPBELL.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,406,920 Stalker Sept. 3, 1946 2,408,632 Griflith Oct. 1, 1945 2,463,864 Gibson Mar. 8, 1949 2,464,651 Pecker Mar, 15, 1949 FOREIGN PATENTS Number Country Date 404,817 Great Britain Jan. 25, 1934 497,048 Great Britain Dec. 12, 1938 504,718 Great Britain April 26, 1939 807,110 France Oct, 12, 1936 

